Both magnetic and optical disk recorders employ either a large plurality of concentric record tracks or a single spiraling record track. The tracks on optical disks are identified by any one of a plurality of surface configurations on the optical medium (disk). A common configuration is a disk-shaped medium having circularly concentric groove or a single spiral groove, for indicating the location of the record tracks. In both magnetic and optical disks recorders, means are provided for faithfully following an addressed one of the record tracks. When it is desired to scan a track other than a currently scanned track, a track seek operation is provided; that is, the track following is aborted and a track seek algorithm is employed. Such seeking generally uses an algorithm which causes the effective disconnection of the track following operation.
In the past, when optical disk transducers were moved from a current track to an immediately adjacent track, that one track seek was colloquially referred to as track jumping. Such track jumping was often used for creating stop motion of video signals recorded on an optical disk. One of the recurrent problems of track jumping, as well as multiple track seeks, is to quickly and faithfully move from the currently scanned track to the addressed or target track, whether it be the next adjacent track or several tracks from the current track.
Other track seek operations use a so called velocity loop for the track seek, then switch to a position loop for track following. Other systems provide for disconnecting the track following position loop and supply a bang bang servo set of pulses for jumping to an adjacent track in a so called open loop mode, i.e., the position error feed back is disconnected. Yet other algorithms employ a single servo loop for both track scanning (following) and track seeking.
The King et al., U.S. Pat. No. 2,843,841, shows an optical disk recorder employing phase encoded recording of binary data. King et al. used an open loop pulse for moving the electron beam from scanning a current track to scan an adjacent track. The open loop pulse deflects the beam toward the second adjacent track more than one-half way, whereupon the pulse is terminated. Then the track following position control system takes over and finishes the movement of the beam to the adjacent target track. King et al. in the position controlling loop effect track following using a so-called grey scale. The data tracks are radially spaced apart on the disk with alternate opaque and transparent track position indicators lying between the data tracks. The data track bits on one side of either an opaque or transparent strip are called upsticking bits, while the bits in a track on the other side of the opaque or transparent strips are called downsticking bits. When the position loop is scanning the upsticking bits, then a reduction of light indicates that the beam is too close to an opaque strip in a first or down direction. However, when the beam is scanning the second track on the opposite side of the opaque strip, then a reduction in light indicates a track deviance in an up or opposite direction. Accordingly, when the beam is moved from one side of an opaque strip to the other side, the sense of the position error track following loop is reversed. The same procedure is followed in switching from a track over a transparent strip. The operation of track jumping in King et al. finds the open loop pulse moving the beam more than half way between the two adjacent tracks. Before termination of the open loop pulse, the sense of the track following loop is reversed. The track following position error signal has a one-half cycle of vibration when the beam is switched from a current track to an immediately adjacent track. The King et al. system appears to be satisfactory for relatively low track densities, but is not satisfactory for the higher track densities contemplated for the present day optical disk recorders.
An improvement over the King, et al. system is shown in U.S. Pat. Nos. 3,473,164 and 3,480,919 to Jensen et al. Rather than having concentric circular tracks as in King et al., Jensen shows a linear raster of tracks, but using the same data track configuration. With particular reference to FIG. 5 of U.S. Pat. No. 3,480,919, it is seen that the King, et al. open loop pulse is replaced by a clamping operation in a differential position error signal loop which forces the electron beam to move in one direction or another toward a second adjacent track. At the same time the clamping action is provided, the sense of the track following position sensing loop is reversed. When the electron beam is about halfway in its movement from the current track to an adjacent track, the clamping is removed. The track following loop completes the movement of the beam to the target adjacent track. This new arrangement provided for a more faithful jump from a current track to an adjacent track. However, the data format is the same and tends to limit the track density of the optical tracks; hence, it is not necessarily suitable for present day contemplated optical disks.
U.S. Pat. No. Re. 32,051 shows track jumping in a video recorder wherein the position error signal produced while traversing between two adjacent tracks is sinusoidal. The zero crossing of the sinusoid at the midpoint between the track causes termination of a jumping pulse. The jumping pulse disconnects the track following loop from an actuator, which in turn is reconnected after the beam has moved more than one-half way from the current track to the target adjacent track. Compensation pulses are provided at the terminous of the jump for reducing overshoot and beam settling time. In acquiring the tracking mode on the adjacent target track it is desired to provide a simpler, but more effective track jumping than provided by the reissue patent.
Hirano, U.S. Pat. No. 4,613,963 shows another open loop jumping circuit which requires a plurality of beams for achieving the open loop jump. It is desired that the use of a plurality of radiation beams be avoided when controlling track following and track seeking.
Matla in U.S. Pat. No. 4,217,612 shows a servo system which uses the same servo loop for both track following or scanning and track seeking. The command signal input into a scanner is changed to switch from track seeking to following. This arrangement will not work in systems not employing a simulator.